Abstract
The dynamics of cell morphology in eukaryotes is largely controlled by small GTPases of the Rho family. Rho GTPases are activated by guanine nucleotide exchange factors (RhoGEFs), of which diffuse B-cell lymphoma (Dbl)-like members form the largest family. Here, we surveyed Dbl-like sequences from 175 eukaryotic genomes and illuminate how the Dbl family evolved in all eukaryotic supergroups. By combining probabilistic phylogenetic approaches and functional domain analysis, we show that the human Dbl-like family is made of 71 members, structured into 20 subfamilies. The 71 members were already present in ancestral jawed vertebrates, but several members were subsequently lost in specific clades, up to 12% in birds. The jawed vertebrate repertoire was established from two rounds of duplications that occurred between tunicates, cyclostomes, and jawed vertebrates. Duplicated members showed distinct tissue distributions, conserved at least in Amniotes. All 20 subfamilies have members in Deuterostomes and Protostomes. Nineteen subfamilies are present in Porifera, the first phylum that diverged in Metazoa, 14 in Choanoflagellida and Filasterea, single-celled organisms closely related to Metazoa and three in Fungi, the sister clade to Metazoa. Other eukaryotic supergroups show an extraordinary variability of Dbl-like repertoires as a result of repeated and independent gain and loss events. Last, we observed that in Metazoa, the number of Dbl-like RhoGEFs varies in proportion of cell signaling complexity. Overall, our analysis supports the conclusion that Dbl-like RhoGEFs were present at the origin of eukaryotes and evolved as highly adaptive cell signaling mediators.